Hybrid magnet configuration

Abstract

A co-axial magnet configuration for the production of a magnetic field and investigational volume which is suitable for measurement of magnetic resonance has at least one superconducting solenoid coil or solenoid coils which are radially nested within each other, wherein the windings of the solenoid coil(s) in a radial region about the axis of the magnetic configuration are disposed between r1 and r2, wherein r1<r2 is characterized in that the windings are surrounded by at least one rotationally symmetric magnet body made from ferromagnetic material which extends over a radial region between r3 and r4 wherein r3<r4 wherein r2<r3<1.3 r2 and r4>1.3 r3, wherein the rotationally symmetric magnet body or bodies are structured, dimensioned and positioned in such a fashion that the magnetic field is homogenized in the investigational volume and the magnetic fringe field outside the magnet configuration is essentially suppressed to permit the production of strong magnetic fields of high homogeneity without requiring notches in the coil configuration.

Description

[0001]This application claims Paris Convention priority of DE 10 2004 007 291.4 filed Feb. 14, 2004 the entire disclosure of which is hereby incorporated by reference.BACKGROUND OF THE INVENTION[0002]The invention concerns a coaxial magnet configuration for production of a magnetic field in an investigation of volume which is suitable for measurement of magnetic resonance with at least one superconducting solenoid coil or with solenoid coils which are radially nested within each other, wherein the windings of the solenoid coil (s) in a radial region about the axis of the magnet configuration are disposed between r1 and r2 wherein r1>r2.[0003]The magnetic field h(z) as a function of the coordinate z on the axis of a magnet system of this kind can be generally expressed as follows:h(z)=h0+h1z+h2z2+h3z3+h4z4+h5z5+h6z6+[0004]The term h0 thereby represents the desired position independent and therefore homogenous magnetic field. The additional terms with the coefficients h1, h2 . . . ...

AI Technical Summary

Benefits of technology

The invention relates to a magnet configuration for a field device used in magnetic resonance imaging (MRI). The technical effects of the invention include achieving a more homogeneous magnetic field and suppressing the stray field outside of the magnet configuration. The magnet body is designed to have a uniform magnetic field and a negative magnetic field term in a specific region of the magnet configuration. The field forming device, which includes at least one ring-shaped element group, helps to achieve a precise fine tuning of the homogeneity of the magnet field. The use of a single solenoid coil and a cylindrically shaped ferromagnetic sheet simplifies the construction of the field device. The magnetic body and the field forming device can be positioned close to the axis of the magnet configuration, making it more compact and cost-effective. The magnetic body and the field forming device can be designed to produce a negative magnetic field term in a specific region of the magnet configuration. Overall, the invention provides a more efficient and compact magnet configuration for MRI applications.

Problems solved by technology

However, solenoid coils are not suitable for production of homogenous magnetic fields, since this simple geometry has, up to this point, not been capable of compensating for the interfering coefficients h2, h4, . . . . It is therefore conventional in the art to use solenoid coils having one or more notches in order to produce homogenous magnetic fields with such windings.

A substantial disadvantage of utilization of magnet coils having notches which, in practice, are fashioned by rings filled up with a solid material, is that the bordering windings made from superconducting wire can undergo a transition into the normally conducting state in response to the large magnetic forces which lead to friction or other relaxation phenomena in the bordering region.

As a result thereof, an overheating of the normally conducting regions can occur and, in extreme cases, the magnet coil can be destroyed.

This makes, in particular, the production of extremely high magnetic fields difficult or makes the magnetic coil more expensive, since one is forced to limit the current strength through the wires in order to keep the magnetic forces which act on the superconducting wire in the regions bordering a notch sufficiently small.

The magnet configuration is consequently provided with a correspondingly greater number of windings of expensive superconducting wire and the entire configuration becomes radially larger, which finally limits the maximum achievable magnetic induction in the investigational volume.

An additional problem with magnet configurations is that they produce highly undesirable magnetic fringe fields in a region of up to 10 m about the magnet configuration.

However, towards this end, additional windings of superconducting wire are required as well as a support body for the shielding windings as a result of which the magnet configuration becomes more complicated, larger, and more expensive.

This configuration has the disadvantage that the weight of the magnet configuration is very high due to the large ferromagnetic cylindrical jacket and, in addition, produces an undesirable influence on the homogeneity of the field.

Images